Process for removal of contaminants from industrial streams

ABSTRACT

A method and system for removing from an aqueous system which is contaminated therewith: (1) mercury present as colloids, ions and/or organically bound compounds, and (2) hydrocarbons solubilized, dispersed, and/or emulsified in the said system. Pursuant to the invention the aqueous system to be treated (such as “produced water”) is passed successively through three filtration stages. The first filtration stage is provided with absorption media which effects reduction/removal of dispersed organically bound mercury species and of the dispersed and partially dissolved hydrocarbon phases, as well as of some colloidal mercury and other dissolved metallic species. The second filtration stage utilizes a salt modified reticulated granular filtration media for reduction/removal of slightly dissolved hydrocarbon phases, mercury in colloidal and ionic form and other dissolved metals. The third filtration stage is a polishing stage, which serves to further reduce by electroless or voltaic reduction residual elemental mercury and/or residual colloidal and ionic mercury. At this third stage metallic mercury is incorporated into a metallic matrix from which the mercury may preferably be recovered.

RELATED APPLICATION

This application claims priority from U.S. provisional patentapplication Ser. No. 60/874,915, filed on Dec. 14, 2006.

FIELD OF INVENTION

This invention relates generally to methods and apparatus for removingcontaminants from aqueous systems, and more specifically relates tofiltration methods and devices for removing mercury and organiccompounds from such aqueous systems.

BACKGROUND OF INVENTION

In the course of practicing a wide variety of commercially importantindustrial processes, aqueous process streams (or more generally“aqueous systems”) are produced which are contaminated with perniciousquantities of mercury present as colloids, ions or organically boundcompounds, and with hydrocarbons which are solubilized, dispersed, oremulsified in the aqueous system. The mercury contaminants have provedto be particularly difficult to remove or reduce to levels deemedharmless to humans. This is a problem that has reached very seriousdimensions, in part because even where mercury may initially be presentin low concentrations in sea water, the natural predator-prey relationin the oceanic food chain causes build up of mercury in the large fishspecies widely eaten by humans to a level where e.g. certain types oftuna are now considered unsafe for frequent human consumption,especially by women who are pregnant.

Generally similar concerns exist with respect to hydrocarboncontaminants. Many of these latter noxious contaminants are also amongthe more difficult compounds to remove from aqueous media. Most arecarcinogenic, and yet such compounds must be removed or minimized beforedischarge of the industrial stream in which they may be present in orderto environmentally protect the bodies of water which the dischargeseventually reach.

One type of such hydrocarbon contaminant consists of dispersed oils,which are often present as oil-in-water emulsions. A further source ofcontamination arises from presence in the water of pernicious slightlysoluble organic compounds such as benzene, toluene, xylene, halogenatedhydrocarbons, ethoxylated glycols, etc.

In the present inventor's U.S. Pat. No. 6,180,010 it is disclosed thatthe compositions described in the inventor's U.S. Pat. Nos. 5,437,793;5,698,139; 5,837,146; and 5,961,823, (all of which disclosures arehereby incorporated by reference) have extremely strong affinities forthe aforementioned contaminants in water; and that when aqueous streamscontaining these noxious contaminants are passed through filtrationmedia incorporating these compositions, the contaminants are immobilizedat the media, as a result of which concentration levels of thecontaminants in the filtrate may be reduced to very low values. Theprinciples of these earlier inventions are also applied in the presentinvention, but in a synergistic combination with further contaminantremoval methodology.

An important example of the type of operation to which the presentinvention is directed arises in the operation of oil and gas explorationand drilling facilities maintained upon platforms in natural or otherbodies of water, including so-called “off shore drilling platforms”. Inconducting operations at these platforms industrial streams aredeveloped (often referred to as “produced water”) which by virtue of theprocesses conducted contain comparatively large quantities of mercuryand various organic contaminants, including those mentioned above.

These contaminants must be partially or entirely removed from theindustrial streams before such streams can be safely discharged. Itwill, of course, be understood that this is indeed merely one among verynumerous examples of aqueous sources of polluting mercury and organiccompounds which are of particular interest for the present invention.

Precipitating agents and flocculants have in the past been extensivelyused in batch operations for removal of pollutants, especially whencolloidal suspensions and emulsions are involved. Precipitating agentsare also often used by forming insoluble salts. In the case ofsemi-soluble organic compounds such as phenols and halogenatedhydrocarbons, adsorbents such as activated carbon are among the mostcommon materials used. Large amounts of such materials are oftenrequired due to desorption from the carbon because of the relativesolubility of these compounds. Phenols and halogenated hydrocarbons areexamples of organic materials which behave as organic acids underappropriate conditions. The present invention is in part directed atutilizing these characteristics of acidic organics, such as thosementioned, in order to remove same from the aqueous media in which theyare present, and by use of a continuous process as opposed to batchprocesses.

Although mercury is a naturally occurring element that is presentthroughout the environment, direct exposure to mercury is harmful topeople and wildlife. Power plants and other industrial sources releasemercury pollution into the air. In the U.S., coal-fired power plants arethe largest source of man-made mercury emissions to the air, accountingfor approximately 40% of all mercury emissions. Once in the air, rainand snow deposit mercury into water bodies. Once in the water, mercurybioaccumulates in fish. People and wildlife are exposed to mercuryprimarily through consuming contaminated fish. Exposure to mercury canlead to toxicological effects in animals and humans, such asneurological and kidney disorders. The most sensitive populations arepregnant woman and their unborn children.

With respect to removal of mercury from aqueous systems such as thementioned produced water, activated carbon is currently one of the mostestablished mercury control technologies. Among other things differentforms of mercury absorb at different rates, in consequence of whichactivated carbon is not very efficient at removing elemental mercury.Chemical reduction and air stripping has also been used as a lowconcentration mercury treatment concept for water containing Hg(II). Theprocess consists of dosing the water with low levels of stannouschloride [Sn(II)] to convert the mercury to elemental mercury (Hg⁰). Hg⁰can then be removed from the water by air stripping or sparging. Alsoknown is a process based on photochemical oxidation. This has chieflybeen known for use in treating flue gas wherein ultraviolet (UV) lightis introduced into the flue gas, to convert elemental mercury to anoxidized form (i.e. mercuric oxide, mercurous sulfate, and mercurouschloride). Once in the oxidized form, mercury can be collected inexisting air pollution control devices such as wet SO₂ scrubbers,electrostatic precipitators, and baghouses (fabric filters).

None of the foregoing techniques, however, have been fully successful intreating aqueous systems of the type with which the present invention isconcerned.

SUMMARY OF INVENTION

In accordance with the present invention a method is disclosed forremoving from an aqueous system which is contaminated with: (1) mercurypresent as colloids, ions and/or organically bound compounds, and (2)hydrocarbons solubilized, dispersed, and/or emulsified in the saidsystem. A typical aqueous system to which the invention is applicable isso-called “produced water”. It will, incidentally, be clear from thisexample of an aqueous system amenable to treatment by the presentinvention, that the term “aqueous system” as used herein not onlyencompasses the bulked mass of liquid in such a system, but as well theaqueous vapors that may be associated therewith and are characterized bydispersed fine aqueous droplets.

Pursuant to the invention, the aqueous system to be treated is passedsuccessively through three filtration stages. The first filtration stageis provided with absorption media which effects reduction/removal ofdispersed organically bound mercury species and of the dispersed andpartially dissolved hydrocarbon phases, as well as of some colloidalmercury and other dissolved metallic species. The second filtrationstage utilizes a salt modified reticulated granular filtration media forreduction/removal of slightly dissolved hydrocarbon phases, mercury incolloidal and ionic form, and other dissolved metals. The thirdfiltration stage is a polishing stage, which serves to further reduce byelectroless or voltaic reduction residual elemental mercury and/orresidual colloidal and ionic mercury. At this third stage metallicmercury is incorporated into a metallic matrix from which the mercurymay preferably be recovered.

The first filtration stage preferably comprises a fluid perviousfiltration media which has been infused with an absorption compositioncomprising a homogeneous thermal reaction product of an oil componentselected from the group consisting of glycerides, fatty acids, alkenesand alkynes, and a methacrylate or acrylate polymer component, wherebythe removed contaminants are immobilized at the media.

At the second filtration stage the aqueous system is preferablycontacted with a reticulated granular media comprised of a naturalzeolite, carbon impregnated with the same absorbent compositionspecified for the first filtration stage, and granular activated carbon(GAC). The mechanism at this stage follows a reactive adsorptionprinciple, which is facilitated by the ability of the natural zeolite tomaintain a constant pH conducive to Lewis Acid Base interactions andprecipitation of ionic and low molecular weight organo-mercurycompounds. The said media has preferably been modified by a suitablesalt such as a sulfate, phosphate and/or nitrate of a period I or periodII alkali and or alkaline earth metal. The natural zeolite is activatedin the presence of contamination and provides a gradual release of ionsinto an aqueous system such as produced water/vapor which causesprecipitation of organically bound and ionic mercury. The impregnatedcarbon and the GAC protect the zeolite activator from soluble andsemisoluble organics and also filters out the precipitates fromsolution.

The third filtration stage comprises an electrically conductive metallicmatrix, the metal having an electromotive series position or anelectrovoltaic potential appropriate to effect the reduction of theresidual mercury. Where the reduction is electroless, ionic mercury isselectively reduced and metallic mercury is incorporated into a fixedalloy matrix to form an amalgam. The matrix may comprise a metallicmesh, which further may be in the form of a fine braid. The matrix maybe disposed directly in a canister having an inlet and outlet, or thematrix may be incorporated into a plurality of tubes inside a largercanister, as in the second stage filter. Where the tubes or othercontainers are vertically disposed, the interstices present at thebraided matrix can enable the depositing mercury upon the braid becomingsaturated to result in the excess mercury flowing down the braid by acapillary or wicking action, enabling it to be recovered at anunderlying receptacle or reservoir.

BRIEF DESCRIPTION OF DRAWINGS

The invention is diagrammatically illustrated by way of example in thedrawings appended hereto in which:

FIG. 1 is a schematic block diagram of a filtering system in which thepresent invention may be practiced;

FIG. 2 is a schematic block diagram illustrating a typical arrangementfor the stage 1 filtration portion of the system shown in FIG. 1;

FIG. 3 is a schematic block diagram illustrating a typical arrangementfor the stage 2 filtration portion of the system shown in FIG. 1; and

FIG. 4 is a schematic block diagram illustrating a typical arrangementfor the stage 3 filtration portion of the system shown in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the schematic block diagrams of FIGS. 1 and 2, the generalmethod used in practice of the invention is schematically set forth. Forpurposes of illustration a contaminated stream or influent to be treatedin accordance with the invention may illustratively be assumed to be oneof produced water resulting from an off-shore oil well operation as hasbeen previously discussed. The stream to be treated is characterized bythe inclusion of (1) mercury present as colloids, ions or organicallybound compounds (other dissolved metals may also be present); and (2)hydrocarbons solubilized, dispersed, or emulsified in the said media. Asto item (2), these include acidic organic compounds, which are a maingroup of substances sought to be removed, such as phenols andhalogenated hydrocarbons. Produced streams of the type referred tousually include additional contaminants, which may be important toremove before discharge into a body of water, notably including oilyhydrocarbons and the like. Typical levels of the contaminants in theinfluent are shown in the legend of FIG. 2, i.e. 100 ppm dispersed anddissolved hydrocarbons, and 100 ppb of mercury as colloidal, organicallybound and/or metal ions.

In accordance with the invention the influent stream at stage 1 is thuspassed through an absorption composition-infused filtration media(referred to for convenience herein as an “ACI filtration media”) whichacts to remove substantial quantities of both the mercury items (1) andthe hydrocarbon components (2) mentioned. Thus as is shown in FIG. 2,the typical resultant effluent has been vastly reduced in contaminants,e.g. mercury has been reduces from 100 ppb to 50-60 ppb, and thehydrocarbons from levels of 100 ppm to 10-20 ppm.

The ACI filtration media preferably comprises a fluid perviousfiltration media which has been infused with an absorption compositioncomprising a homogeneous thermal reaction product of an oil componentselected from the group consisting of glycerides, fatty acids, alkenesand alkynes, and a methacrylate or acrylate polymer component, wherebythe oily contaminants are immobilized at the media. Filtration media ofthis type are disclosed in detail in the present applicant's U.S. Pat.No. 6,190,010, the disclosure of which is incorporated herein byreference. As set forth in that U.S. patent, the media (which isinfused) can comprise a non-woven polypropylene, paper, a porousceramic, a porous metal, a mineral particulate such as vermiculite orperlite, or so forth.

The term “absorbent composition” as used herein is one of conveniencefor identifying the said compositions of my aforementioned patent, andwill be used as well in referring to the compositions used in stage I ofthe present invention. The specific mechanism by which the noxiouscontaminants are removed from aqueous streams by conjunctive use of such“absorbent compositions” is not completely understood, and could includeattachment and/or fixation of such contaminants by mechanisms whichtechnically involve various physical and/or chemical interactions. Theterm “absorbent” as used herein is intended to encompass all of thesepossible mechanisms.

The absorbent compositions used herein in the ACI filtration media arealso disclosed in the present inventor's U.S. Pat. Nos. 5,437,793;5,698,139; and 5,837,146, and 5,961,823 (all of which disclosures arehereby incorporated by reference) They have extremely strong affinitiesfor the aforementioned hydrocarbon and also have been found to haveaffinities for the mercury contaminants in water.

Referring to FIGS. 1 and 3, the influent stream having been purified atstage 1 of the bulk of its hydrocarbon components and of substantialportions of its mercury based contaminants then passes to the secondfiltration stage, i.e. that based upon the salt modified reticulatedgranular filtration media. At the second filtration stage the aqueoussystem is preferably contacted with a reticulated granulated granularmedia comprised of a natural zeolite, an ACI filtration media such ascarbon impregnated with the same impregnating absorbent compositionspecified for the first filtration stage, and granular activated carbon(GAC). Such media has preferably been modified by a suitable salt suchas a sulfate, phosphate and/or nitrate of a period I or period II alkalimetal and or alkaline earth metal. At this stage the very slightlysoluble acidic acting organic compounds along with the mercury presentin colloidal and/or ionic forms are removed by the media effecting acidbased neutralization, stripping and reduction, enabling these pollutantsto be removed from the waste stream. The media should preferably becapable of behaving as a base while at the same time having limitedsolubility in water so as to enable performing the neutralization in acontinuous mode.

The streams to be treated by the invention at the second stage arepreferably passed through a canister containing a plurality ofreplaceable tubes, the flow path being arranged to effect passage of thestream to be treated through such tubes. The interior of each tube isprovided in series first with a section of the modifying salt or salts,followed by a section containing the reticulated granular filtrationmedia. Additional sections of the tube may include a prefiltrationsection at the tube input, which contains a filtration media which hasbeen infused with an absorption composition particularly suited forremoval of oily components which may be present in the stream to betreated, and which would possibly foul the salt(s) section. The infusedabsorption media may be of the same type as discussed above for use inthe first stage of the present invention. A post-filtration section atthe output end of the tube may also be present, which again contains aninfused absorption media of the type just indicated. The stream emergingfrom such a post-filtration section can be passed through a sodiumcarbonate or other ion exchange media, so that any remaining earth metalions are exchanged for harmless sodium ions. As indicated in the legendin FIG. 3, the typical effluent then shows that mercury has been reducedto less than 10 ppb, and hydrocarbons to less than 1-10 ppm.

Referring to FIG. 4, the effluent from stage 2 then becomes the influentstream for treatment in the aforementioned third (and final) filtrationstage. The principal purpose of the final stage is to remove residualionic and elemental mercury to less than 0.5 ppb. This level of purityis difficult for adsorptive media and ion exchange media to attain dueto equilibrium effects. Electroless Reduction Technology eliminates theequilibrium effects by reducing and removing mercury. The final stagecan be comprised of modular cartridges consisting of braided copperelements electroplated with a composition of precious metals. Theseelements serve to utilize the redox potential of ionic mercury andcapture and amalgamate the reduced elemental mercury. The braidingallows for directional extraction and collection by exploiting thesurface tension of metallic mercury.

The basic mechanisms involved are:

Accordingly at this polishing stage, electroless or voltaic reductionare used to remove residual elemental mercury and/or residual colloidaland ionic mercury. The third filtration stage comprises an electricallyconductive metallic matrix, the metal of which has an electromotiveseries position or an electrovoltaic potential appropriate to effect thereduction of the residual mercury. Where the reduction is electroless,ionic mercury is selectively reduced and metallic mercury isincorporated into a fixed alloy matrix to form an amalgam. The matrixmay comprise a metallic mesh, which further may be in the form of a finebraid. Such braid may for example consist of braided copper coil whichis electroplated with silver and gold. This matrix material will readilyamalgamate elemental mercury. The matrix may be disposed directly in acanister having an inlet and outlet for the stream being treated, withthe matrix being positioned in the canister to be in the flow path ofthe stream. Similarly the matrix may be incorporated into a plurality oftubes inside a larger canister, as in the second stage filter. Anarrangement of this geometrical type is shown in FIG. 5 of theapplicant's U.S. Pat. No. 7,264,722, except of course that the tubesthere are associated with absorbents, not with metallic matrices foreffecting reduction of mercury. Where the tubes or other containers arevertically disposed, the interstices present at the braided matrix canenable the depositing mercury upon the braid becoming saturated toresult in the excess mercury flowing down the braid by a capillary orwicking action, enabling it to be recovered at an underlying receptacleor reservoir.

The present invention is further illustrated by the following Examples,which are indeed to be considered as merely exemplary and notdelimitative of the invention otherwise described:

Examples I and II

Two samples of produced water were treated in the filtration system ofthe present invention. The samples were subjected to analysis as rawinputs and after being subjected to the method of the invention, i.e. tofiltration by successive treatment at all three stages of the system ofFIG. 1. For comparison the samples were also analyzed after filtrationusing various combinations of the stages of the present filtrationsystem. In all instances the analysis were conducted using EPA method1664. The results of these tests are shown in the below Table. Themarked reductions in all of the contaminants will be evident.Particularly to be noted is the vast reduction in mercury, including theextremely effective action of stage 2 and the further polishing effectachieved after passing through stage 3, i.e. the electroless reductionstage. Note too here that where the electroless reduction stage is usedalone the mercury reduction is very small, and thus it will be evidentfrom this and the remaining data that a truly synergistic effect hasbeen achieved by use in sequence of the three stages pursuant to theinvention.

Example I Example II ACI ACI, ACI ACI, ER After and ACI and SMRGM ERAfter and ACI and SMRGM Raw only ACI ER SMRGM and ER Raw only ACI ERSMRGM and ER O&G ppm 26.1 NA 9.9 NA ND ND 24.8 NA 8.7 NA ND ND SVOC ppm157 NA 75 NA 0.044 0.044 56 NA 67.8 NA 0.087 0.087 VOC ppm 36 NA 25 NAND ND 36 NA 22 NA ND ND Hg ppb 63.6 55 23 22 1.1  0.46  41 37 17.1 17.31.1  0.46  Total ppm 219.1 116.8 Organics O&G = oil and gas; SVOC =semi-volatile organic compounds; VOC = volatile organic compounds; SMRGM= salt modified reticulated granular media; ER = electroless reduction

While the present invention has been set forth in terms of specificembodiments thereof, the instant disclosure is such that numerousvariations upon the invention are now enabled to those skilled in theart, which variations yet reside within the scope of the presentteaching. Accordingly, the invention is to be construed by broadlyinterpreting the scope and spirit of the present disclosure.

1. A method for removing from aqueous media contaminated with: (1)mercury present as colloids, ions or organically bound compounds, and(2) hydrocarbons solubilized, dispersed, or emulsified in the saidmedia; comprising: passing the said media in successive order through(a) a first filtration stage comprising an absorption media whicheffects reduction/removal of dispersed organically bound mercuryspecies, colloidal mercury, and dispersed and partially dissolvedhydrocarbon phases, said first stage comprising a fluid perviousfiltration media which has been infused with an absorption compositioncomprising a homogeneous thermal reaction product of an oil componentselected from the group consisting of glycerides, fatty acids, alkenesand alkynes, and a methacrylate or acrylate polymer component, wherebyremoved contaminants are immobilized at the media; (b) a secondfiltration stage comprising a salt modified reticulated granularfiltration media for reduction/removal of slightly dissolved hydrocarbonphases, and mercury in colloidal and ionic form; said salt beingselected from one or more members of the group consisting of a sulfate,phosphate and/or nitrate of a period I or period II alkali metal oralkaline earth metal; and (c) a third filtration stage comprising anelectroless or voltaic actuated electrically conductive metallic matrixfor reducing residual ionic mercury by electroless or voltaic reduction,and for extracting the reduced mercury and residual elemental and/orcolloidal mercury by collection at the matrix, the metal of said matrixhaving an electromotive series position or an electrovoltaic potentialappropriate to effect the reduction of the residual ionic mercury.
 2. Amethod in accordance with claim 1, wherein the aqueous media comprisesproduced water.
 3. A method in accordance with claim 1, wherein thereduction is electroless, ionic mercury being selectively reduced andmetallic mercury being incorporated into a fixed alloy matrix to form anamalgam.
 4. A method in accordance with claim 3, wherein said matrixcomprises a mesh.
 5. A method in accordance with claim 4, wherein saidmesh is braided.
 6. A method in accordance with claim 5, wherein thebraided mesh comprises braided copper coil which is electroplated withsilver and gold.